1. Field of the Invention
The present invention relates to magnetic bubble domain memory systems in general and more particularly to control means for generating synchronized control signals for carrying out memory and logic functions.
2. Description of the Prior Art
In the field of electronic computers and other data processing devices, the performance of such systems is largely limited by the speed, capacity and reliability of the memory system. Various types of memory systems are known and have been used in the art, such as disc files, magnetic tapes, ferrite cores and etc. Recently significant interest has been directed toward a different type of memory wherein data is stored in the form of magnetic "bubbles" moving in thin films of magnetic material. The bubbles are actually cylindrical magnetic domains whose polarization is opposite to that of the thin magnetic film in which they are embedded. The bubbles are stable over a considerable range of conditions and can be moved from one point to another at high velocity. Interest in these devices in large part is based on the high packing density that can be achieved and the ability of the cylindrical domain to be independent of the boundary of the magnetic material in the plane in which it is formed and hence capable of being moved anywhere in the plane of the magnetic material to effect various memory and logic functions. Such devices are described in an article by Andrew H. Bobeck and H.E.D. Scoville entitled "Magnetic Bubbles", Scientific American, June 1971, Vol. 224, pp. 88-90. This article describes several structures for manipulating and controlling transmission of magnetic bubbles along discrete paths and includes an explanation of one form of a magnetic bubble domain memory.
A magnetic domain can be manipulated by programming currents through a pattern of conductors positioned adjacent the magnetic material or by varying the magnetic field surrounding the magnetic material. As an example, the magnetic domains or bubbles may be formed in thin platelets having uniaxial anisotrophy with the easy magnetic axis perpendicular to the plate comprising such material as rare earth orthoferrites, rare earth aluminum and gallium substituted iron garnets or rare earth cobalt. Since the magnetic domains can be propagated, erased, replicated and manipulated to form logic operations and their presence and absence detected, the magnetic domains may be utilized to perform many of the on/off or digital functions vital to computer operation.
Magnetic bubble domain memory systems offer significant advantages since logic, memory, counting, and switching can all be performed within a single layer of solid magnetic material. This is in contrast to conventional memory systems in which information must move from one device to another through interconnecting conductors and high gain amplifiers.
Many organizations of magnetic domain memories have been disclosed. As an example, U.S. Pat. No. 3,618,054 discloses a major-minor loop memory organization. Typically, the major loop is closed and is established by an arrangement of T-bar or chevron Permalloy circuits on an orthoferrite or garnet crystal platelet. The bubble domains are moved around the loop by a magnetic field which rotates in the plane of the magnetic material. The major loop is generally elongated such as to allow a number of minor loops to be aligned along side. Two-way transfer gates permit the transfer of magnetic domains from the minor loop to the major loop and from the major loop to the minor loops. Data information stored in the minor loops is first circulated until the desired word (comprised of one bit from each loop) reaches the transfer points. On command of a transfer signal, the information is transferred to a major loop whereupon it can be simply read out or erased and overwritten. The data is then further advanced along the major loop in response to the rotating magnetic field and transferred back into the minor loops.
The major-minor loop organization permits a synchronized pattern of domains in the corresponding minor loops to represent a binary word. The propagation of domains in the loops is synchronous so as to permit parallel transfer of a selected word into the major loop by the simple expedient of keeping track of the number of rotations of the in-plane magnetic field to determine the proper instant of transfer.
In order to carry out the memory functions, such as logic operations, reading, writing and etc., it is necessary to drive electrical current through appropriate leads on the magnetic bubble domain chip at precisely timed intervals relative to the in-plane rotating field present at the chip's surface. The electrical currents must be applied at precise times in order to maintain synchronous operations. These currents are effective to control the magnetic bubble domains in such a way so as to allow the user to write data into the chip at desired locations and also to read data from desired locations.
Typically, the control signals for synchronizing memory operations for a magnetic bubble domain memory system are generated by one-shot multivibrators which depend on RC discharge circuits in order to produce pulses at desired intervals during each rotation of the in-plane rotating magnetic fields. Various problems, however, have been encountered in utilizing one-shot multivibrators for generating these control signals. First, timing control circuits comprising one-shot multivibrators are relatively expensive. One contributing factor to the relatively large expense is the fact that a large number of parts are required in order to provide the required number of control signals. Not only are the parts themselves expensive but since a large number of parts is required, the assembly and test costs associated therewith are also substantial. Secondly, the large number of discrete parts requires a substantial amount of space and makes the overall system larger than would be desired. Thirdly, the reliability is reduced as a result of the large number of parts and assembly and test operations required. Fourthly, it is difficult to get reproducibility of the control signals over different operating conditions because the component values vary with temperature fluctuations. Further it is difficult to select resistors and capacitors for the RC timing circuits that are exactly of the same value. As a result, there will be some variation between the different control signals caused by manufacturing tolerances in component values.
Accordingly, it is an object of the present invention to provide improved timing control for a magnetic bubble domain memory system.
A further object of the invention is to provide means for generating control signals for magnetic bubble domain memory systems which is more compact, less expensive and more reliable than conventional one-shot multivibrator RC discharge circuits.
An additional object of the present invention is to utilize a non-volatile digital memory for generating control signals for a magnetic bubble domain memory system.